The conventional railway car truck in use in North America for several decades has been the three-piece truck, comprising a pair of parallel side frames oriented longitudinally and connected by a transversely mounted bolster. The bolster is supported on the side frames by spring sets. The wheel sets of the truck are received in bearing adapters placed in leading and trailing pedestal jaws in the side frame. The railway car is mounted on the center plate of the bolster, which allows the truck to pivot with respect to the car.
Braking systems for the railway car transmit force from a pneumatic or hydraulic actuator to cause the brake shoes to be applied against the wheels. Such systems may comprise “foundational” rigging, having components distributed on the railway car, or alternatively, may be mounted on the truck in a truck-mounted system. In either case, there is always a premium on the available space on the car body or on the truck for the necessary components so that the parts do not interfere with other systems on the railway car.
A truck-mounted braking system typically comprises two brake beams transversely mounted with respect to a longitudinal axis of the railway car and having brake shoes on opposite ends. Each brake beam typically comprises a compression member and a tension member connected in the middle by a strut. The brake beams may be connected by a brake actuator assembly comprising an actuator (such as an air cylinder) mounted on one of the beams, and a push rod oriented longitudinally between the brake beams, so that when the brake is applied, the brake actuator assembly forces the beams apart, causing force to be transmitted to the brake shoes which press against the wheels. The truck-mounted system is characterized by having fewer elements between the brake actuator and the wheels, compared to a foundational rigging system.
A conventional truck-mounted brake system may also comprise a slack adjuster assembly, as disclosed in U.S. Patent Application Publication No. 2016/0229428 to Sunde, which is incorporated by reference in its entirety. The slack adjuster may be mounted in tandem with the brake actuator assembly, such that the brake actuator assembly and the slack adjuster are connected to the respective brake beams by a pair of levers. The slack adjuster transmits force between the brake beams and adjusts the distance between the brake beams to accommodate for wear on the brake pads. It is characteristic of the truck-mounted systems that the slack adjuster and the brake actuator are situated between the levers on opposed brake beams.
Braking ratio is the ratio of braking force applied on the railway car wheels to the weight of the railway car. The American Association of Railroads (“AAR”) sets a standard (AAR S-401-99) for the brake ratio for a loaded car at a maximum of 14%, and for an empty car at 32%. In addition, the AAR requires a minimum braking ratio of 11% for an air brake and 10% for a hand brake. The danger of exceeding braking ratios is that the brake shoes may become locked against the wheels, so that the wheels fail to turn and are pushed along the rails. Therefore, it is desired to be able to adjust the brake force applied against the wheels depending on the lading condition of the railway car.
Braking systems for railway cars universally include a hand brake, operated manually and independently of the pneumatic brake system. A hand brake for a foundational brake rigging system is described in U.S. Pat. No. 7,896,140 to Heitmeyer, incorporated by reference. A hand brake (and hand brake lever) for a truck-mounted braking system is described in U.S. Pat. No. 6,702,073 to Sommerfeld, also incorporated by reference. In a truck-mounted system, the hand brake may be connected to one end of the live lever, actuated manually, usually to secure an unattended or unpowered car against unplanned movement, i.e., as a “parking brake”. Thus the hand brake is capable of operating even when the pneumatic brake is not on line. Conventionally, the hand brake applies the same force to the wheels whether the car is loaded or unloaded, being independent of the brake pneumatics.
So-called “empty load devices” are known which operate in conjunction with pneumatic systems, to maintain braking forces below a certain brake ratio depending on the sensed weight of the car. U.S. Pat. No. 4,080,005, which is incorporated by reference, discloses an empty load fluid pressure brake system with a proportioning valve, operated with compressed air. By way of example and not limitation, a mechanical empty load device used with a foundational brake rigging system is disclosed in U.S. Pat. No. 3,690,420 to Natschke, which is also incorporated by reference. The braking systems disclosed in this patent is characterized by an outboard arrangement of the load sensing device and the brake actuator.
Further examples of a truck-mounted braking system of the type described above are provided in U.S. Patent Application Publication No. 2011/0147140 to Ring, and U.S. Pat. No. 7,802,662, also incorporated by reference in their entirety. These additional disclosures teach various methods and apparatuses for preventing or limiting brake lock-out and for monitoring and controlling travel of the brake elements generally.